package outbox

import (
	"context"
	"database/sql"
	"log/slog"
	"time"

	"atlas9.dev/c/core/dbi"
)

type OutboxWorker struct {
	DB            *sql.DB
	Outbox        func(dbi.DBI) Consumer
	Consumers     []string
	Handler       func(ctx context.Context, event Event, task Task) error
	Interval      time.Duration
	LeaseDuration time.Duration
	MaxAttempts   int
	BatchSize     int
}

func (w *OutboxWorker) Run(ctx context.Context) {
	for {
		if ctx.Err() != nil {
			return
		}

		processed := w.poll(ctx)
		if !processed {
			select {
			case <-time.After(w.Interval):
			case <-ctx.Done():
				return
			}
		}
	}
}

func backoff(attempts int) time.Duration {
	d := time.Duration(1<<attempts) * time.Second
	if d > 5*time.Minute {
		d = 5 * time.Minute
	}
	return d
}

func (w *OutboxWorker) poll(ctx context.Context) bool {
	processed := false
	for _, consumer := range w.Consumers {
		if w.pollConsumer(ctx, consumer) {
			processed = true
		}
	}
	return processed
}

func (w *OutboxWorker) pollConsumer(ctx context.Context, consumer string) bool {
	batchSize := w.BatchSize
	if batchSize <= 0 {
		batchSize = 1
	}

	var claimed []Claimed
	err := dbi.ReadWrite(ctx, w.DB, func(tx dbi.DBI) error {
		var e error
		claimed, e = w.Outbox(tx).Claim(ctx, consumer, w.LeaseDuration, batchSize)
		return e
	})
	if err != nil {
		slog.Error("claiming tasks", "consumer", consumer, "err", err)
		return false
	}
	if len(claimed) == 0 {
		return false
	}

	for _, c := range claimed {
		err := w.Handler(ctx, c.Event, c.Task)
		if err != nil {
			slog.Error("processing event",
				"type", c.Event.EventType,
				"consumer", c.Task.Consumer,
				"attempts", c.Task.Attempts,
				"err", err)

			nackErr := dbi.ReadWrite(ctx, w.DB, func(tx dbi.DBI) error {
				store := w.Outbox(tx)
				if w.MaxAttempts > 0 && c.Task.Attempts >= w.MaxAttempts {
					return store.Fail(ctx, c.Event.Seq, consumer)
				}
				retryAfter := time.Now().Add(backoff(c.Task.Attempts))
				return store.Nack(ctx, c.Event.Seq, consumer, &retryAfter)
			})
			if nackErr != nil {
				slog.Error("nacking task", "err", nackErr)
			}
			continue
		}

		err = dbi.ReadWrite(ctx, w.DB, func(tx dbi.DBI) error {
			return w.Outbox(tx).Complete(ctx, c.Event.Seq, consumer)
		})
		if err != nil {
			slog.Error("completing task", "err", err)
		}
	}

	return true
}